Rare Z-decay into light pseudoscalar bosons in the simplest little Higgs model

TL;DR

This paper investigates rare Z-boson decay modes involving a light pseudoscalar boson predicted by the simplest little Higgs model, finding some decay channels with branching ratios potentially observable at future colliders.

Contribution

It provides a detailed analysis of Z-boson decay modes into light pseudoscalars within the simplest little Higgs model, highlighting which modes could be experimentally detectable.

Findings

Branching ratios for Z→b̄bη and Z→τ̄τη can reach 10^{-7} and 10^{-8}, respectively.

Branching ratios for Z→ηγ can reach 10^{-8}, potentially observable at GigaZ.

Other decay modes like Z→ηηη and Z→ηgg have much lower branching ratios, making them less accessible.

Abstract

The simplest little Higgs model predicts a light pseudoscalar boson $\eta$ and opens up some new decay modes for $Z$-boson, such as $Z \to \bar{f} f \eta$, $Z\to \eta\eta\eta$, $Z\to \eta\gamma$ and $Z\to \eta gg$. We examine these decay modes in the parameter space allowed by current experiments, and find that the branching ratios can reach $10^{-7}$ for $Z\to \bar{b}b\eta$, $10^{-8}$ for $Z\to \bar{\tau}\tau\eta$, and $10^{-8}$ for $Z\to \eta\gamma$, which should be accessible at the GigaZ option of the ILC. However, the branching ratios can reach $10^{-12}$ for $Z\to \eta\eta\eta$, and $10^{-11}$ for $Z\to \eta gg$, which are hardly accessible at the GigaZ option.